WO2025217374A1 - Systems and methods for determining adjustments to a position or orientation of an implant relative to a bone - Google Patents

Abstract

A system and method for determining adjustments to a position or orientation of an implant relative to a bone such as to stabilize a knee in mid-flexion. Assessing native and/or planned joint gaps for a knee joint procedure to balance the knee in mid- flexion may involve determining one or more changes to a planned implant component position and/or orientation relative to a bone that achieves an intended spatial relationship to the gaps between the bones throughout the knee's range-of-motion such as a more rectangular shape compared to the shape of the distances prior to the changes.

Description

SYSTEMS AND METHODS FOR DETERMINING ADJUSTMENTS TO A

POSITION OR ORIENTATION OF AN IMPLANT RELATIVE TO A BONE

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This PCT application claims the benefit of United States Provisional Patent Application No. 63/635,087 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 17, 2024 and claims the benefit of United States Provisional Patent Application No. 63/633,479 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 12, 2024, each of which is hereby incorporated herein by reference in its entirety.

[0002] The subject matter of this patent application may be related to the subject matter of commonly-owned PCT Application No. PCT/US2022/046146 filed October 10, 2022 and published as PCT Publication No. WO/2023/059931 on April 13, 2023, which claims priority from United States Provisional Patent Application No. 63/253,923 filed October 8, 2021, each of which is hereby incorporated herein by reference in its entirety. The subject matter of this patent application also may be related to the subject matter of commonly-owned U.S. Provisional Patent Application No. 63/542,624 filed October 5, 2023, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0003] The present invention generally relates to computer-assisted surgery, and more particularly to a system and method for determining adjustments to a position or orientation of an implant relative to a bone such as to stabilize a knee in mid-flexion.

BACKGROUND OF THE INVENTION

[0004] Throughout a lifetime, bones and joints become damaged and worn through normal use, disease, and traumatic events. Arthritis is a leading cause of joint damage that overtime leads to cartilage degradation, pain, stiffness, and bone loss. Arthritis can also cause the muscles articulating the joints to lose strength and become painful.

[0005] If the pain associated with the dysfunctional joint is not alleviated by less- invasive therapies, a joint arthroplasty procedure is considered as a treatment. Joint arthroplasty is an orthopedic procedure in which an arthritic or dysfunctional joint surface is replaced with an orthopedic implant.

[0006] The accurate placement and alignment of an implant is a large factor in determining the success of joint arthroplasty. In total knee arthroplasty (TKA), the articulating surfaces of the knee joint are replaced with prosthetic components, or implants, typically formed of metal or plastic, to create new articulating joint surfaces. The implants include contact surfaces intended to contact bone. TKA requires the removal of worn or damaged articular cartilage and bone on the distal femur and proximal tibia to form surfaces (“cut surfaces”) on the remaining bone to contact the contact surfaces of the implant. The position and orientation (POSE) of the cut surfaces determine the final placement and POSE of the implants within the joint. Generally, surgeons plan and create the cut surfaces so the final placement of the implants restores the mechanical axis or kinematics of the patient’s leg while preserving the balance of the surrounding knee ligaments. Even small implant alignment errors outside of clinically acceptable ranges correlate with worse outcomes and increased rates of revision surgery.

[0007] Current TKA implants are designed to be installed using specific manual instrumentation (e.g., cutting jigs, cutting blocks, alignment fixtures) to form the cut surfaces. Femoral implants typically have five femoral contact surfaces and one or more stabilizing features (e.g., pegs, boxes). The five femoral contact surfaces are intended to contact five cut surfaces on the remaining femur. The stabilizing features of a femoral implant may include pegs or a box to stabilize the femoral implant on the femur. The pegs or box are intended to be inserted into stabilizing cut features (e.g., holes) cut into the bone, typically through a cut surface of the femur and are typically formed perpendicular to a cut surface. For example, FIGs. 1A - 1C illustrate a patient’s distal femur ‘F’ and a contour matching femoral implant 12 for a TKA procedure, where five contact surfaces on the implant are intended to contact five cut surfaces on the femur ‘F’. The anterior cut surface 14 is intended to contact the anterior contact surface 13, the anterior chamfer cut surface 16 is intended to contact the anterior chamfer contact surface 15, the distal cut surface 18 is intended to contact the distal contact surface 17, the posterior chamfer cut surface 20 is intended to contact the posterior chamfer contact surface 19, and the posterior cut surface 22 is intended to contact the posterior contact surface 21. The femoral implant 12 also includes stabilizing features in the form of pegs (23, 24) intended to be inserted into stabilizing cut features (e.g., holes, not shown) formed into the distal cut surface 18 of the femur 10. The articulating surface 16 (or outer surface) of the femoral implant 12 is also shown, where the articulating surface 16 is intended to contact a portion of the tibial implant and articulate relative thereto as the patient flexes and extends their knee. Tibial implants typically have one tibial contact surface and a stabilizing feature (e.g., a keel). The one tibial contact surface is intended to contact one cut surface on the remaining tibia. The stabilizing features of a tibial implant may include a keel to stabilize the tibial implant on the tibia. The keel is intended to be inserted into a stabilizing cut feature (e.g., a hole) that is cut into the bone, typically through the cut surface of the tibia, and is typically formed perpendicular to the cut surface.

[0008] Computer-assisted surgical (CAS) devices (e.g., surgical robots) have been developed to assist in forming the cut surfaces on the femur and tibia. Examples of these CAS devices are the RIO Robotic Arm (Stryker/Mako), the TSolution One Surgical System (THINK Surgical), the TMINI Miniature Robotic System (THINK Surgical), and the ROSA Surgical System (Zimmer). All of these systems generally include planning software for planning the location of an implant with respect to the bone. The planning software includes 3-D models of the patient’s bones, at least one 3- D model of an implant, and software tools that allow the user to position the implant models relative to the bone models. The CAS device then executes the plan to assist in forming the cut surfaces on the bone to mount the implant thereon in the planned position and orientation (POSE).

[0009] Another important aspect of performing a successful TKA procedure is assessing the soft tissues (e.g., ligaments) that surround the knee. For example, it is important to account for the tension and laxity of the ligaments when the implants are placed in the knee. One technique for assessing the soft tissues to account for the tension in the ligaments is gap balancing, where the gaps between the femur and the tibia are evaluated with the knee in both flexion and extension. This is illustrated in FIGs. 2A and 2B. FIGs. 2A and 2B depict a femur ‘F’ and tibia ‘T’ in full extension (FIG. 2A) and in flexion (FIG. 2B), respectively. One of the goals of gap balancing is to obtain an equal gap (medial gap = lateral gap) between the bones in both flexion and extension, as depicted by the rectangles 30 and 32. Another goal of gap balancing is to achieve an extension gap 26 that equals, or closely matches, the flexion gap 28. If the gaps aren’t balanced, the user may choose to adjust the planned location for a bone cut. For example, the user may rotate the implant internally or externally to obtain an equal medial-lateral gap in flexion, and varus or valgus to obtain an equal medial-lateral gap in extension. The user may also move the implant distally or proximally to decrease or increase the size of the gap in extension, or posterior or anterior to decrease or increase the size of the gap in flexion, to make sure there is enough room for the implants to fit in the knee and that the ligaments will be properly tensioned when the implants are positioned in the knee.

[0010] There remains at least one issue that is not currently addressed with current gap balancing techniques. Surgeons still have concerns and challenges tied to mid-flexion instability, and how to plan the placement of the implant to avoid this mid-flexion instability. Mid-flexion instability is a big complaint from patients post-operatively.

SUMMARY OF VARIOUS EMBODIMENTS

[0011] In accordance with one embodiment of the invention, a system, method, and computer program product performs processes for assessing native and/or planned joint gaps for a knee joint procedure to balance the knee in mid-flexion including at least determining one or more changes to a planned implant component position and/or orientation relative to a bone that achieves an intended spatial relationship to the gaps between the bones throughout the knee’s range-of-motion.

[0012] In various alternative embodiments, the intended spatial relationship may be a more rectangular shape compared to the shape of the distances prior to the changes. Determining one or more changes may involve changing different degrees of freedom either as individual degrees of freedom or in combination and evaluating the resulting gaps. The processes may include an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the gaps, in which case determining one or more changes may involve permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function. The processes may include an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component. Each planned joint gap may be measured as a distance from at least one point on a planned location for forming a cut surface on a tibial bone model to at least one point on a surface of a femoral implant model. The processes may include displaying a graph that shows the distance for one or more of the gaps, together or separately, throughout the knee’s range-of-motion. The graph may show the gap distances between a planned location for forming a proximal cut surface on a tibia bone model to a planned location of an outer surface of a femoral implant model at a plurality of angles throughout the knee’s range-of-motion. Assessing the gaps may involve affixing tracking arrays to the bones and tracking locations of the bones via the tracking arrays.

[0013] In various alternative embodiments, the processes may include determining one or more alternative implant component positions and/or orientations based on the assessment of the native and/or planned joint gaps. The processes may include displaying the alternate implant component positions and/or orientations relative to the bone models on a display device and optionally also may include displaying other informative data including measurements.

[0014] In accordance with one embodiment of the invention, a system, method, and computer program product performs processes for computer assisted surgery including determining locations of a first bone model and a second bone model that correspond to determined locations of a first bone and a second bone, respectively, as the first bone and the second bone are moved to a plurality of angles within a range-of-motion (ROM) of the first bone relative to the second bone; determining a distance between a point associated with the first bone model and a point associated with the second bone model for each angle from the plurality of angles using the determined locations of the first bone model and the second bone model; making adjustments to a planned location for a first implant model relative to the first bone model or a planned location for a second implant model relative to the second bone model; updating one or more distances between the point associated with the first bone model and the point associated with the second bone model in response to one or more adjustments; and identifying at least one planned location for the first implant model or planned location for the second implant model where the distances for two or more angles from the plurality angles achieves an intended spatial relationship.

[0015] In various alternative embodiments, the processes may include displaying the distances for at least two angles from the plurality of angles. The point associated with the first bone model may be a point on a surface of a first implant model positioned on the first bone model. The point associated with the second bone model may be a point on a planned location for forming a cut surface on the second bone model. The intended spatial relationship may be a more rectangular shape than the shape of the distances before the adjustments. Making adjustments, updating, and identifying may be performed by an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the distances, in which case determining one or more changes may involve permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function. Making adjustments, updating, and identifying may be performed by an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component. Determining the locations of the first bone and the second bone may be performed using a tracking system that determines the locations of the first bone and the second bone by determining the locations of a first tracking array affixed to the first bone and a second tracking array affixed to the second bone.

[0016] Additional embodiments may be disclosed and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Those skilled in the art should more fully appreciate advantages of various embodiments of the invention from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below.

[0018] FIGs. 1A - 1C illustrate a patient’s distal femur ‘F’ and a contour matching femoral implant 12 for a TKA procedure, where five contact surfaces on the implant are intended to contact five cut surfaces on the femur ‘F’.

[0019] FIGs. 2A and 2B depict a femur ‘F’ and tibia ‘T’ in full extension (FIG. 2A) and in flexion (FIG. 2B), respectively. [0020] FIG. 3 shows a graphical user interface (GUI) for planning a TKA procedure in accordance with certain embodiments.

[0021] FIG. 4 depicts a GUI 40 for assessing the gaps while gap balancing the knee in the operating room in accordance with one embodiment.

[0022] FIG. 5 depicts the GUI 40 for balancing the gaps in the mid-flexion range in accordance with certain embodiments.

[0023] FIG. 6 is a schematic view showing a computer-assisted surgical system 200 including a 2-DoF device 100, a computing system 204, and a tracking system 206.

[0024] FIGS. 7A and 7B are schematic views showing the 2-DoF device 100 in greater detail.

[0025] It should be noted that the foregoing figures and the elements depicted therein are not necessarily drawn to consistent scale or to any scale. Unless the context otherwise suggests, like elements are indicated by like numerals. The drawings are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0026] As discussed above, there remains at least one issue that is not currently addressed with current gap balancing techniques. Surgeons still have concerns and challenges tied to mid-flexion instability, and how to plan the placement of the implant to avoid this mid-flexion instability. Mid-flexion instability is a big complaint from patients post-operatively. Thus, there exists a need for a system and method to determine adjustments to the planned placement of an implant to achieve more balanced gaps throughout the range-of-motion of the patient’s knee.

[0027] Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety.

[0029] The following description provides examples related to knee replacement; however, it should be appreciated that the embodiments described herein are readily adapted for use in a myriad of applications where it is desirous to position implants for joint replacement procedures in other portions of the body.

[0030] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range from 1 to 4 is intended to include such ranges as 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4.

[0031] Unless indicated otherwise, explicitly or by context, the following terms are used herein as set forth below.

[0032] As used herein, like reference numerals described in with respect to subsequent drawings have the meaning imparted thereto with respect to the previously detailed drawings.

[0033] As used herein, the term “bone data” refers to data related to one or more bones. The bone data may be determined: (i) prior to making modifications (e.g., bone cuts, insertion of a pin or screw, etc.) to one or more bones, referred to as pre-operative bone data; and/or (ii) determined after one or more modifications have been made to a bone, referred to as post-modification bone data. The bone data may include: the shapes of the one or more bones; the sizes of the one or more bones; angles and axes associated with the one or more bones (e.g., epicondylar axis of the femoral epicondyles, longitudinal axis of the femur, the mechanical axis of the femur); angles and axes associated with two or more bones relative to one another (e.g., the mechanical axis of the knee); anatomical landmarks associated with the one or more bones (e.g., femoral head center, knee center, ankle center, tibial tuberosity, epicondyles, most distal portion of the femoral condyles, most proximal portion of the femoral condyles); bone density data; bone microarchitecture data; and stress/loading conditions of the bone(s). By way of example, the bone data may include one or more of the following: an image data set of one or more bones (e.g., an image data set acquired via fluoroscopy, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, other x-ray modalities, laser scan, etc.); three-dimensional (3-D) bone models, which may include a virtual generic 3-D model of the bone, a physical 3-D model of the bone, a virtual patient-specific 3-D model of the bone generated from an image data set of the bone; and a set of data collected directly on the bone intra-operatively commonly used with imageless CAS devices (e.g., laser scanning the bone, painting the bone with a digitizer, digitizing boney landmarks). The term “virtual” may also be referred to herein as “digital”, meaning the data is stored, generated, and/or processed by a computer.

[0034] As used herein, the terms “computer-assisted surgical device” and “CAS device” refer to devices used in surgical procedures that are at least in part assisted by one or more computers. Examples of CAS devices illustratively include tracked/navigated instruments and surgical robots. Examples of a surgical robot illustratively include robotic hand-held devices, serial-chain robots, bone mounted robots, parallel robots, or master-slave robots, as described in U.S. Patent Nos. 5,086,401; 6,757,582; 7,206,626; 8,876,830; 8,961,536; 9,707,043; and 11,457,980; which patents and patent application are incorporated herein by reference. The surgical robot may be active (e.g., automatic/autonomous control), semi-active (e.g., a combination of automatic and manual control), haptic (e.g., tactile, force, and/or auditory feedback), and/or provide power control (e.g., turning a robot or a part thereof on and off). It should be appreciated that the terms “robot” and “robotic” are used interchangeably herein. The terms “computer-assisted surgical system” and “CAS system” refer to a system comprising at least one CAS device and may further include additional computers, software, devices, or instruments. An example of a CAS system may include: i) a CAS device and software (e.g., cutting instructions, pre-operative bone data) used by the CAS device); ii) a CAS device and software (e.g., surgical planning software) used with a CAS device; iii) one or more CAS devices (e.g., a surgical robot); iv) a combination of i), ii), and iii); and iv) any of the aforementioned with additional devices or software (e.g., a tracking system, tracked/navigated instruments, tracking arrays, bone pins, rongeur, an oscillating saw, a rotary drill, manual cutting guides, manual cutting blocks, manual cutting jigs, etc.). [0035] Also referenced herein is a “surgical plan.” A surgical plan is generated using planning software. The surgical plan may be generated pre-operatively, intra- operatively, or pre-operatively and then modified intra-operatively. The planning software may be used to plan the location for an implant with respect to a bone and/or plan a location to make one or more modifications (e.g., bone cuts, location for inserting bone pins) to the bone. The planning software may include various software tools and widgets for planning the surgical procedure. This may include, for example, planning:

(i) a location for implant data (e.g., a 3-D implant model) with respect to bone data (e.g., a 3-D bone model) to define a location for the implant with respect to the bone;

(ii) a location for one or more bone cuts to be made relative to bone data to define the locations for forming one or more cut surfaces on the bone, and/or (iii) one or more locations for inserting hardware (e.g., bone pins, screws) relative to bone data. All of which may be used to define locations for robot operating instructions (e.g., a cut-file, a virtual plane, virtual boundary, a virtual axis) with respect to the bone data, where a CAS device is directed to control movement of an end-effector (e.g., the hardware, a burr, end-mill, drill bit) with respect to the bone according to the robot operating instructions.

[0036] As used herein, the term “digitizer” refers to a device capable of measuring, collecting, recording, and/or designating the position of physical locations (e.g., points, lines, planes, boundaries, etc.) in three-dimensional space. By way of example but not limitation, a “digitizer” may be: a “mechanical digitizer” having passive links and joints, such as the high-resolution electro-mechanical sensor arm described in U.S. Patent No. 6,033,415 (which U.S. patent is hereby incorporated herein by reference); a non-mechanically tracked digitizer probe (e.g., optically tracked, electromagnetically tracked, acoustically tracked, and equivalents thereof) as described for example in U.S. Patent 7,043,961 (which U.S. patent is hereby incorporated herein by reference); an end-effector of a robotic device; or a laser scanner.

[0037] As used herein, the term “digitizing” refers to the collecting, measuring, designating, and/or recording of physical locations in space using a digitizer. In some embodiments, “digitizing” may refer to the conversion of a designated location, area, or volume in space to a digital format. For example, a tracking system may determine the location of a digitizer probe tip in contact with a point on the bone, where the determined location of that point is saved to computer memory.

[0038] As used herein, the term “registration” refers to: the determination of the spatial relationship between two or more objects; the determining of a coordinate transformation between two or more coordinate systems associated with those objects; the mapping of an object onto another object; and a combination thereof. Examples of objects routinely registered in an operating room (OR) illustratively include: CAS systems/devices; anatomy (e.g., bone); bone data (e.g., 3-D virtual bone models); a surgical plan (e.g., location of virtual planes defined relative to bone data, cutting instructions defined relative to bone data, or other robot operating instructions defined relative to bone data); and any external landmarks (e.g., a tracking array affixed to a bone, an anatomical landmark, a designated point/feature on a bone, etc.) associated with the bone (if such landmarks exist). Methods of registration known in the art are described in U.S. Pat. No. 6,033,415; 8,010,177; 8,036,441; and 8,287,522; and 10,537,388. In particular embodiments with orthopedic procedures, the registration procedure relies on the manual collection of several points (i.e., point-to-point, point- to-surface) on the bone using a tracked digitizer where the surgeon is prompted to collect several points on the bone that are readily mapped to corresponding points or surfaces on a 3-D bone model. The points collected from the surface of a bone with the digitizer may be matched using iterative closest point (ICP) algorithms to generate a transformation matrix. This transformation matrix and various other transformation matrices provides the mathematical locational relationship between: (i) bone data (e.g., a 3-D bone model, planned location for forming one or more cut surfaces; planned location for an implant model relative to a bone model); and/or a surgical plan (e.g., a pre-defined location for a targeted virtual plane that was defined with respect to bone data, a pre -defined location of robot operating instructions that was defined with respect to bone data); and (ii) the coordinate system of a tracking array affixed to the bone (if present); or a CAS device (e.g., the base coordinate system of the CAS device, or a coordinate system of a tracking array affixed to the CAS device and, if needed, calibration data and/or kinematic data that define the location of an end-effector relative to the tracking array); and any other coordinate system or object required to perform the procedure. In other embodiments, the registration is performed using imageless registration.

[0039] As used herein, the term “display” is intended to encompass a variety of the digital devices that during operation provide an image (including multiple images in succession to form a video feed) recognizable to human viewing. Digital devices operative herein as displays illustratively include a graphical user interface (GUI), a computer or television (TV) monitor, a holographic display, a mobile display, a smartphone display, a video wall, a head-mounted display, a heads-up display, a virtual reality headset, a broadcast reference monitor, any of the aforementioned with a touchscreen capability, and a combination thereof. One or more computers comprising a processor may be operatively coupled to the display for controlling the output of the display.

[0040] As used herein, the term “feedback” may refer to visual feedback provided on a display. This “feedback” may also be provided in other forms, which may be in lieu of or in addition to visual feedback. For example, the “feedback” may include audio feedback, haptic/tactile feedback (e.g., a buzz or vibration when a digitizer tip is located at in an area of max deviation), or other visual feedback (e.g., a light on the surgical device may turn green or red depending on the amount of error between the surgical device and a planned cut surface).

[0041] Embodiments of the present invention describe a system and method for determining adjustments to a planned position or orientation of implant data (e.g., an implant model) relative to bone data (e.g., a bone model) that will stabilize the knee in mid-flexion. Mid-flexion instability is a common complaint from patients post- operatively and surgeons currently have a difficult time planning the placement of the implant that avoids such mid-flexion instability.

[0042] Therefore, certain embodiments of the invention include a graph that shows the gap distances between the planned location for forming the proximal cut surface on the tibia bone model to the planned location of the outer surface of the femoral implant model at a plurality of angles throughout the range of motion (ROM) of the knee. It should be the case that there is an ideal shape to the graph (e.g., a rectangular shape), which shows relatively equal gap distances throughout flexion (except possibly near the end of the flexion range, where the graph might flare due to femoral rollback). The ideal graph shape should really be the case whether or not the knee is tensioned on both the medial and lateral sides during the range of motion.

[0043] Conventionally, if the surgeon did not see this ideal graph shape, for example the middle section of the graph after tensioning throughout the range is bumped out or bulging, rather than being straight, this could be an indication of a risk of mid-flexion instability as a result of the currently planned implant positions and the surgeon does not know how to change the plan to address this problem.

[0044] Therefore, certain embodiments computationally determine how to change the plan in order to achieve the ideal shape of this graph. In accordance with certain embodiments of the present invention, the plan change might be achieved by running an optimizer that changes the different degrees of freedom, like the tibia slope angle, either as individual degrees of freedom or in combination, and evaluate the resulting graph shapes to find the best one, i.e., the one that produces the straightest results, except for, or even including, the flare at the end caused by femoral rollback. In accordance with other embodiments, the plan change might be achieved using an artificial intelligence (Al) or machine learning (ML) approach with appropriate training, giving the surgeon certain measurements to help understand how to make the plan change decisions. The plan change could be achieved in other ways.

[0045] The above computation may include traditional optimization and/or AI/ML. For but one example, the optimizer method could define a cost function of difference from rectangular of the graph shape, and then permute the positions or orientations of the femoral implant model and/or tibial implant model in one or more degrees-of-freedom (DoF) (possibly 6 DoF) relative to their respective bone models, in a gradient decent type of approach, to get the minimum cost, i.e., the most rectangular solution.

[0046] Without limitation, the overall goal is to optimize the plan to achieve the desired graph shape, yet maintain as best as possible the gap measurements, or other criteria that may be based on surgeon preferences, which may help improve outcomes by reducing mid-flexion instability for TKA patients.

[0047] It should be appreciated, that conventional “gap balancing” techniques are but one means to an end, where the end is ligament tension profiles throughout flexion and/or other dynamic motion of the knee, such that the knee kinematics throughout the motion result in the patient perception that the knee is behaving ‘normally,’ including an absence of pain. There are other means to achieving this same end with techniques other than gap balancing to assess the surrounding soft tissues and ligament tension profdes. Thus, the present invention may not be limited to conventional gap balancing techniques or simple variations thereof. Embodiments described herein may be adapted to other techniques for achieving mid-flexion motion stabilization.

[0048] With reference now to FIG. 3, a graphical user interface (GUI) 40 is shown for planning a TKA procedure. The GUI 40 is operated by planning software for planning the location for forming cut surfaces on the bone to mount an implant on the bone in a desired POSE. The planning software may include models of the femur and tibia (also referred to as a femoral bone model 42 or tibial bone model 44), which may have been generated from an image data set (e.g., CT scan data) of the patient’s bones. In a particular embodiment, the planning software may include two planning modes. The first planning mode may include a library of 3-D implant models that are supported by the system to allow the user to plan the position and orientation (POSE) for mounting an implant relative to a bone. The second planning mode (as shown in FIG. 3) is for planning TKA procedures with an implant agnostic system as described in U.S. Prov. Pat. App. No. 63/542,624 assigned to the assignee of the present application (incorporated by reference above). In the first planning mode, the GUI 40 may include a drop-down menu for a user to select a desired implant make, model, and size. The GUI 40 may then display the selected implants in the form of a femoral implant model 46 relative to a femoral bone model 42 and a tibial implant model 48 relative to a tibial bone model 44. The GUI 40 may include a plurality of software tools, or widgets, that allow the user to adjust the position and orientation of the implant models relative to the bone models to designate the best fit and alignment for mounting the implant onto the bone. In other embodiments, the planning software may automatically determine a position and orientation for mounting the implant on bone based on a user’s planning preferences/philosophy (e.g., neutral mechanical axis alignment vs. kinematic alignment). The planned location for mounting the implant model relative to the bone model defines the planned locations for forming the cut surfaces on the bone (e.g., the planned location for forming distal cut surface is known based on where the distal contact surface of the femoral implant model overlaps with the femoral bone model). The GUI may display graphics 49 (e.g., line, box, grayed out bone areas) showing the planned locations of the cut surfaces, or the bone models may be updated show the cut surfaces directly on the bone models. The GUI 40 may also display alignment information in the relevant degrees-of-freedom to assist in planning the position for mounting the implant on the bone. This information may include the degrees of varus- valgus of the bone with respect to the mechanical axis as a result of a planned distal cut surface, the degrees of external-internal rotation of the implant from a bone condylar axis (e.g., transepicondylar axis (TEA), posterior condylar axis (PC A)) as a result of the planned posterior cut surface, the degrees of flexion-extension of the implant with respect to the bone as a result of the planned distal cut surface and/or planned posterior cut surface, the tibial posterior slope of the implant with respect to the bone as a result of the planned tibial cut surface, etc. The GUI may also display an amount of bone that will be resected for a given bone cut (e.g., 7.0 mm on the lateral distal condyle and 4.5 mm on the medial distal condyle as shown in the top left window of the GUI 30 of FIG. 3). After the user is satisfied with the planned location for mounting the implant on the bone, the plan is saved for future use.

[0049] FIG. 4 depicts a GUI 40 for assessing the gaps while gap balancing the knee in the operating room in accordance with one embodiment. In this embodiment, before gap balancing, a first tracking array is affixed to the femur and a second tracking array is affixed to the tibia. The respective bone models are then registered to the femur and tibia in the coordinate system of the tracking arrays affixed to each bone using techniques known in the art. For example, the bone models of the femur and tibia may be registered to the locations of each bone, respectively, by matching points digitized on the bone with corresponding points/surfaces on the corresponding bone model. The registration process outputs transformation matrices that transform the location of the bone models to the location of the bones in the coordinate system of the respective tracking array affixed thereto. Since the planned location of the cut surfaces were defined relative to the bone models in the planning software, the registration process also registers the planned location for forming the cut surfaces to the real-time locations of each bone, respectively. Likewise, the planned location for implant data (e.g., a 3-D implant model, geometry data about the implant) may be transformed relative to the planned location for forming the cut surfaces on the bone models. Therefore, the planned location for mounting the implant data on the cut surfaces may also be determined relative to the real-time location of the physical bones. A tracking system (or computer operatively coupled to the tracking system) may therefore determine locations and movement of the bone models, the planned location for forming cut surfaces, and the planned location for mounting implant data on the cut surfaces, all corresponding to the real-time locations and movement of the femur “F’ and tibia ‘T’. [0050] To perform gap balancing, the user applies tension to the surrounding ligaments, e.g., by placing a tensioner between the two bones or by pulling the tibia away from the femur to force tension on the ligaments. While applying tension on the ligaments, the user flexes and extends the knee throughout the knee’s range of motion (e.g., 0 degrees is fully extended and as much as the knee can flex >0 degrees). It should be noted that gap balancing may occur before any bone cuts are made, or in some cases, the user may choose to make the tibia bone cut first and then perform gap balancing. The tracking system records the locations of the bones via the tracking arrays affixed thereto throughout this motion and may determine the corresponding locations of at least one of the registered bone models, the planned location for forming the cut surface, and the implant data. In some embodiments, the GUI 31 may display the femoral bone model 42 and tibial bone model 44 and movement of these bone models corresponding to the real-time location and movement of the bones. The GUI 31 may also display the planned locations of the cut surfaces and/or the planned location for the implant models relative to the bone models and movement of such corresponding to the real-time location and movement of the bones.

[0051] A computer operating software operatively coupled to the tracking system may then determine the medial and lateral gaps. In a particular embodiment, the gap balancing is performed before any cuts are made. In this embodiment, the computer may determine the medial and lateral gaps throughout the ROM of the knee, where the gap measurement at each angle in the ROM is between: (i) one or more points (45, 51) on the surface of the planned location for forming the proximal cut surface 48 on the tibia bone model 44; and (ii) one or more points (47, 49) on the outer surface of the femoral implant model 46 as mounted (or transformed) onto the planned locations for forming the cut surfaces on the femoral bone model 42. For each angle in the ROM, the distance is calculated using a different point (e.g., the closest point(s) on the outer surface of the femoral implant model to the planned location for forming the proximal cut surface 48 on the tibial bone model 44) on the outer surface 16 of the femoral implant model 46 to accurately represent the gap distance for that angle. For example, point 47 on the outer surface of the femoral implant model 46 is used to calculate the gap distance when the knee is in extension, which is the closest points to the planned location for forming the proximal cut surface 48 on the tibial bone model 44 at that extension angle. Then point 53 on the outer surface of the femoral implant model 46 is used to calculate the gap distance when the knee is in flexion, which is the closest point to the planned location for forming the proximal cut surface 48 on the tibial bone model 44 at that flexion angle. The location of the one or more points on the proximal cut surface 48 of the tibial implant model 44 may or may not change. The location of the point on the proximal cut surface 48 may change for each angle in the ROM such that the shortest distance between the outer surface of the femoral implant model 46 and the proximal cut surface 48 is always calculated. Determining and showing the gaps as a measurement between the planned location for forming the tibia proximal cut surface and the outer surface of the femoral implant allows the user to better assess the true gaps that will result between the bones in this mid-flexion range because the outer surface of implant is curved in this mid- flexion range. This is in contrast to conventional systems that determine and show the gaps in mid-flexion as being between the proximal tibia cut surface and the posterior chamfer cut surface on the femur, which may add a lot of variability and noise to the measurements and doesn’t account for the curved geometry of the implant in this mid-flexion range. However, it should be appreciated, that embodiments of the present invention may also include different points for measuring the gap distances. For example, the gaps may be measured between: (i) one or more points on the surface of the tibial bone model and one or more points on the surface of the femoral bone model; (ii) one or more points on the surface of the tibial implant model and one or more points on the surface of the femoral implant model; (iii) one or more points on a planned location for any other cut surface on a bone model and one or more points on an implant model; or (iv) any other combination of measurements between points on an implant model, a bone model, or a planned location of a cut surface. The points for measuring the gap distances may also include points located on cut surfaces formed on the bone (e.g., a point on the femoral distal cut surface 18 formed on the femur ‘F’, or a point on the proximal tibia cut surface formed on the tibia ‘T’). [0052] The computer may calculate the gaps using tracking data from the tracking system and the transformations described above. For example, tracking data from the tracking system may include the real-time locations of the tracking array affixed to the femur and the tracking array affixed to the tibia. The tracking data and transformation matrices are then used to determine the locations of: (i) the femoral bone model, the planned location for forming the femoral cut surfaces, and/or the planned location for mounting the femoral implant model relative to the femoral bone model; and (ii) the tibial bone model, the planned location for forming the proximal cut surface, and/or the planned location for mounting the tibial implant model relative to the tibial bone model; all of which will correspond to the real-time locations of the femur ‘F’ and tibia ‘T’. For each angle in the ROM, the computer determines the location of the one or more points (45, 51) on the proximal cut surface 48 and the one or more points (47, 49) on the outer surface of the femoral implant model 46 for calculating the gap distance(s) between the corresponding points (e.g., point 45 to point 47 (medial gap in extension), point 51 to point 49 (lateral gap in extension), and point 51 to point 53 (lateral gap in flexion)). The gap distances may be calculated in real-time as the user flexes and extends the patient’s knee to populate the numbers on the graph shown on the right.

[0053] The graph on the right shows an example of the determined gaps at a plurality of flexion-extension angles in the ROM, where the pattern filled bars on the right are examples of lateral gap measurements and the filled bars on the left are examples of medial gap measurements. The y-axis is the flexion-extension angle, and in this example, ranges from a minimum of 0° (extension) to a maximum of 120° (full flexion). The x-axis is the measured gap in millimeters, which, in this example, ranges from 0 at the center of the graph to 20 millimeters in both the medial and lateral directions. Note, the magnitudes of these numbers are provided for illustrative purposes only; each patient presents differently. One of the goals of gap balancing is to obtain an equal gap (medial gap = lateral gap) in both flexion and extension. As shown in FIG. 4, the gaps with the knee in extension (0°) are equal on the medial and lateral side, and the gaps with the knee in flexion (120°) are also equal on the medial and lateral side. The gaps are also equal in flexion and extension. However, the gaps in the mid-flexion range 50 bulge out and are larger than that in extension and/or flexion. This may indicate that the knee is prone to mid-flexion instability as a result of the currently planned locations for mounting the implants on the bones. The mid-flexion range 50 may include flexionextension angles from 20° to 80°, 30° to 70°, 40° to 60°, or anywhere in those ranges. Also shown in FIG. 4 is the implant alignment information from the surgical plan. For the femur, this may include the amount of distal resection, the amount of posterior resection, the implant coronal alignment, the implant rotational alignment, and the implant flexion-extension alignment. For the tibia, this may include the amount of proximal resection, the tibial slope, and the implant internal-external rotation.

[0054] FIG. 5 depicts the GUI 40 for balancing the gaps in the mid-flexion range in accordance with certain embodiments. A computer operating software may computationally determine how to change the currently planned location for mounting the implant on the bone to achieve an intended (or desired) shape of the graph (e.g., a more rectangular shape 52 to the gap distances compared to the gap distances prior to the changes). The software may include an optimizer algorithm that changes or adjusts the positions and/or orientations of the implant data (e.g., implant model) relative to the bone data (e.g., bone model), either in individual degrees-of-freedom or in combination, to find a solution that produces an intended graph shape (e.g., a rectangular graph shape). For example, the algorithm may adjust the tibia slope angle, the distal or proximal location of the femoral implant, the anterior or posterior location of the femoral implant, the flexion-extension rotation of the femoral implant, the internalexternal rotation of the femoral implant model, etc. For each change, or combination of changes, the algorithm determines the new gap distances from the previously recorded gap distances (e.g., the gap distances recorded while the user flexed and extended the knee throughout the ROM as shown and described with respect to FIG. 4) as result of the change and may update the shape of the graph to show the user the effect of the change on the gap distance. For example, if the algorithm adjusts the femoral implant model by 1 millimeter distally, then the algorithm reduces the gap distance in extension by 1 millimeter from the previously recorded gap distance. For each change, or combination of changes, the algorithm then evaluates the resulting graph shape to find the best change(s) that result(s) in the intended graph shape (e.g., one or more changes to the implant model position and/or orientation that produces the straightest, or most rectangular graph shape). In a particular embodiment, the optimizer algorithm works by defining a cost function of difference from the intended graph shape, and then permutes the positions and/or orientations of the femoral implant model and tibial implant model relative to their respective bone models, in one or more degrees-of- freedom (DoF), in a gradient decent type of approach, to achieve the minimum cost (e.g., the most rectangular solution). It should be appreciated that while many surgeons might agree that the best or intended graph shape is a rectangular shape, this might not always be the case. Surgeons who are highly skilled in biomechanics analysis might have other goals to the intended graph shape. For example, some surgeons might prefer a solution where there are equal gaps medially in extension, laterally in extension, and medially in flexion (at 90 degrees), but that laterally in flexion, the gap should be larger than those 3, resulting in an intended graph shape that is trapezoidal. Therefore, the optimizer algorithm may be programmed to change the planned implant position to achieve an intended graph shape as desired by the surgeon. For example, the optimizer algorithm may be programmed to achieve a rectangular graph shape or a trapezoidal graph shape depending on the preference of the user. The system may include an input mechanism for the user to input their desired graph shape preference (e.g., what graph shape they prefer) into the system.

[0055] FIG. 5 also shows the proposed changes to the implant alignment information resulting from the optimizer algorithm as well as the new gaps (as shown in the graph) that would be achieved by those changes. In this example, the optimizer algorithm proposes small changes to the femoral distal resections, femoral posterior resections, femoral implant rotational alignment, and tibial slope. The mid-flexion gaps in the graph no longer bulge out, the overall shape of the graph is more rectangular, and the medial and lateral gaps remain equal in flexion and extension.

[0056] In other embodiments, the software may include artificial intelligence (Al) algorithms or machine learning (ML) algorithms to achieve the best graph shape. The AI/ML algorithms may be appropriately trained to change the position and/or orientation of the implant model relative to the bone model to achieve the best graph shape. The AI/ML may alternatively provide the user with certain measurements to help them understand how to make changes to the implant position and/or orientation themselves that would achieve the best graph shape.

[0057] In some cases, there may be a flare of the gaps when the knee is at maximum flexion angles caused by femoral rollback. In some embodiments, the algorithm considers the flared gaps at these maximum flexion angles to achieve the best graph shape at these maximum flexion angles, while in other embodiments, the algorithm ignores the flared gaps in its calculations.

[0058] In some embodiments, the optimizer algorithm or AI/ML algorithm may be consider one or more constraints or weighting criteria to achieve a desired result for the user. The constraints or weighting criteria may be pre-programmed in the algorithm, or provided as a user input to the algorithm. For example, a particular user may have a specific gap target or a specific gap range in flexion and extension (e.g., a gap between 17 - 20 mm in flexion and extension). In this case, the user may input this gap range into the software, where the algorithm uses this input to produce the best graph shape that also achieves the specific gap range. Other constraints or weighting criteria may include: equal medial and lateral gaps in flexion and extension; equal gaps in flexion and extension; maintaining a particular degree-of-freedom of the implant relative to the bone (e.g., maintaining the coronal alignment, rotational alignment, femoral implant flexion-extension angle, etc.); maintaining the joint line; and a limit to an amount of change (e.g., no more than 5° change to the tibial slope, no more 2° to the rotational alignment, etc.). In some embodiments, the constraints or weighting criteria may prohibit changes to the implant model position that are known to cause mid-flexion instability. For example, a tibial slope angle over a certain amount may be known to cause mid-flexion instability. In this case the algorithm may be pre-programmed not to exceed this tibial slope angle, and/or provide an alert to the user if a change to the implant position exceeds the slope angle. Other alerts can also be provided, which may give the algorithm more freedom to produce one or more different plans that the user can then compare, and the alerts may sway the user to select one plan over another.

[0059] FIG. 5 also depicts an implant adjustment tool 54 in the form of an interactive graphical user interface element that can be manipulated, e.g., using a mouse, touchscreen input, etc. The implant adjustment tool 54 allows the user to make incremental changes to the implant model position and/or orientation relative to the bone model, e.g., to make manual changes to the implant position and/or orientation to achieve a more rectangular graph shape and/or to fine-tune the gaps after the optimizer algorithm or AI/ML algorithm has been executed. The software may update the measured gaps in the graph when the user makes a manual adjustment to the implant position and/or orientation, and these updates can be made and presented to the user in real-time such that the user can receive immediate feedback regarding each incremental change. In this respect, the implant adjustment tool 54 could be used to make adjustments prior to or during a surgical procedure.

[0060] Referring now to FIGs. 6, 7A, and 7B, embodiments of the present inventive system and method generally includes a computer-assisted surgical system. In some inventive embodiments, a 2-DoF device 100 is provided for maintaining alignment of an end-effector 206 (e.g., drill bit, saw blade, bone pin) coincident with a virtual plane. FIG. 6 is a schematic view showing the computer-assisted surgical system 200 including a 2-DoF device 100, a computing system 204, and a tracking system 206. In other inventive embodiments, the system includes an end effector 306 extending from a robotic arm.

[0061] The computing system 204 generally includes hardware and software for executing a surgical procedure. By way of example but not limitation, in one preferred form of the present invention, the computing system 204 is configured to control the actuation of the working portion 104 relative to the hand-held portion 102 of the 2-DoF 100 device to maintain alignment of the end-effector axis 307 coincident with a virtual plane defined in a surgical plan. The end-effector 206 coupled to the working portion 104 in operation modifies (e.g., inserts pins, cuts, mills, etc.) subject bone. The computing system 204 may generate control signals to accurately maintain the endeffector axis 207 coincident with a virtual plane defined in the surgical plan based on: a) the location of the virtual plane as registered to the location of the bone (or more specifically to the coordinate system of a tracking array affixed to the bone); and b) the tracked POSE of the 2-DoF device 100.

[0062] The computing system 204 of the computer-assisted surgical system 200 may include: one or more device computers (208, 209) including a planning computer 210; a tracking computer 211, and peripheral devices. Each computer may include one or more processors. Processors operate in the computing system 204 to perform computations and execute software associated with the inventive system and method described herein. The device computer(s) (208, 209), the planning computer 210, and the tracking computer 211 may be separate entities as shown in FIG. 6, or it is also contemplated that operations may be executed on one (or more) computers depending on the configuration of the computer-assisted surgical system 200. For example, the tracking computer 211 may have operational data to control the 2-DoF device 100 without the need for a device computer (208, 209). Furthermore, if desired, any combination of the device computers (208, 209), planning computer 210, and/or tracking computer 211 may be connected together via a wired or wireless connection. It is further appreciated that one or more of the computers may be readily located remote from the surgical site. Cloud-based computation is also contemplated in the present invention.

[0063] The peripheral devices allow a user to interface with the computing system 204 and may include, but are not limited to, one or more of the following: one or more userinterfaces, such as a display or monitor (212a, 212b) to display a graphical user interface (GUI); and user-input mechanisms, such as a keyboard 214, mouse 222, pendent 224, joystick 226, and foot pedal 228. If desired, the monitor(s) (212a, 212b) may have touchscreen capabilities, and/or the 2-DoF device 100 may include one or more input mechanisms (e.g., buttons, switches, etc.). Another peripheral device may include a tracked digitizer probe 230 to assist in the registration process. A tracking array 220c is assembled to the digitizer probe 230 to permit the tracking system 206 to track the POSE of the digitizer probe 230 in space. The digitizer probe 230 may further include one or more user input mechanisms to provide input to the computing system 204. For example, a button on the digitizer probe 230 may allow the user to signal to the computing system 204 to digitize a point in space to assist in registering a bone to a surgical plan.

[0064] The device computer(s) (208, 209) may include one or more processors, controllers, software, data, utilities, and/or storage medium(s) such as RAM, ROM or other non-volatile or volatile memory to perform functions related to the operation of the 2-DoF device 100. By way of example but not limitation, one or more of the device computers (208, 209) may include software to control the 2-DoF device 202, e.g., generate control signals for the actuators to move the working portion 104 relative to the hand-held portion 102 to a targeted POSE, receive and process tracking data, control the rotational or oscillating speed of the end-effector 306 by controlling motor 305, execute registration algorithms, execute calibration routines, provide workflow instructions to the user throughout a medical procedure, as well as any other suitable software, data or utilities required to successfully perform the procedure in accordance with embodiments of the invention.

[0065] In some embodiments, the system 200 may include a first device computer 208 located separate from the 2-DoF device 100 and a second device computer 209 housed in the 2-DoF device 100 to provide on-board control. The first device computer 208 may be dedicated to the control of the surgical workflow via a GUI, the registration process and the associated calculations, the display of 3-D models and 3-D model manipulation or animation, as well as other processes. In particular embodiments, the first device computer 208 comprises software for assessing the gaps during gap balancing and balancing the knee in mid-flexion as described above. In particular, the software is programmed with an optimizer algorithm or an AI/ML algorithm for determining one or more changes to an implant position and/or orientation relative to a bone that achieves a more rectangular shape to the gaps between the bones throughout the knee’s range-of-moti on. The second device computer 209, also referred to herein as an on-board device computer, may be dedicated to the control of the 2-DoF device 100. For example, the on-board device computer 209 may compute and generate the control signals for the actuator motors (210a, 210b) based on: i) received signals/data corresponding to the real-time POSE of the 2-DoF device 100 from the tracking system; and ii) received signals/data corresponding to the real-time POSE of the virtual plane computed by first device computer 208. The on-board device computer 209 may also send internal data (e.g., operational data, actuator/screw position data, battery life, etc.) via a wired or wireless connection. In some inventive embodiments, wireless optical communication is used to send and receive the signals/data described herein. Details about bi-directional optical communication between a 2-DoF device 100 and a tracking system 206 are further described below.

[0066] The planning computer 210 in some inventive embodiments is dedicated to planning the procedure. By way of example but not limitation, the planning computer 210 may contain hardware (e.g., processors, controllers, memory, etc.), planning software, data, and/or utilities capable of: receiving, reading, and/or manipulating medical imaging data; segmenting imaging data; constructing and manipulating three- dimensional (3D) virtual bone models; storing and providing computer-aided design (CAD) files such as implant CAD files; planning the POSE for cut surfaces, virtual planes, screws, pins, implants, grafts, and fixation hardware relative to pre-operative bone data; generating the surgical planning data for use with the system 200, and providing other various functions to aid a user in planning the surgical procedure. The final surgical plan data may include one or more images of a bone or virtual models of the bone, registration data, subject identification information, the POSE for inserting or mounting one or more pins, screws, implants, grafts, fixation hardware relative to the bone, the POSE for forming one or more cut surfaces on the bone, the POSE for executing robot operating instructions, and/or the POSE of one or more virtual planes defined relative to the bone. The device computer(s) (208, 209) and the planning computer 210 may be directly connected in the operating room, or the planning computer 210 may exist as separate entities outside the operating room. The final surgical plan is readily transferred to a device computer (208, 209) and/or tracking computer 211 through a wired (e.g., electrical connection) or a wireless connection (e.g., optical communication) in the operating room; or transferred via a non-transient data storage medium (e.g., a compact disc (CD), or a portable universal serial bus (USB drive)) if the planning computer 210 is located outside the operating room (or if otherwise desired). As described above, the computing system 204 may comprise one or more computers, with multiple processors capable of performing the functions of the device computer 208, the tracking computer 211, the planning computer 210, or any combination thereof.

[0067] The tracking system 206 of the present invention generally includes a detection device to determine the POSE of an object relative to the position of the detection device. In particular embodiments of the present invention, the tracking system 206 is an optical tracking system such as the optical tracking system described in U.S. Pat. No. 6,061,644 (which patent is hereby incorporated herein by reference), having two or more optical detectors 207 (e.g., cameras) for detecting the position of fiducial markers arranged on rigid bodies or integrated directly on the tracked object. By way of example but not limitation, the fiducial markers may include an active transmitter, such as an LED or electromagnetic radiation emitter; a passive reflector, such as a plastic sphere with a retro-reflective film; or a distinct pattern or sequence of shapes, lines or other characters. A set of fiducial markers arranged on a rigid body, or integrated on a device, is sometimes referred to herein as a tracking array (220a, 220b, 220c, 312), where each tracking array has a unique geometry/arrangement of fiducial markers, or a unique transmitting wavelength/frequency (if the markers are active LEDS), such that the tracking system 206 can distinguish between each of the tracked objects.

[0068] If desired, the tracking system 206 may be incorporated into an operating room light 218, located on a boom, a stand, or built into the walls or ceilings of the operating room. The tracking system computer 211 includes tracking hardware, software, data, and/or utilities to determine the POSE of objects (e.g., tissue structures, the 2-DoF device 100) in a local or global coordinate frame. The output from the tracking system 206 (i.e., the POSE of the objects in 3-D space) is referred to herein as tracking data, where this tracking data may be readily communicated to the device computer(s) (208, 209) through a wired or wireless connection. In a particular embodiment, the tracking computer 206 processes the tracking data and provides control signals directly to the 2- DoF device 100 and/or device computer 208 based on the processed tracking data to control the position of the working portion 104 of the 2-DoF device 100 relative to the hand-held portion 102. In another embodiment, the tracking computer 206 sends tracking data to a receiver located on the 2-DoF device 100, where an on-board device computer 209 generates control signals based on the received tracking data.

[0069] The tracking data is determined in some inventive embodiments using the position of the fiducial markers detected from the optical detectors and operations/processes such as image processing, image filtering, triangulation algorithms, geometric relationship processing, registration algorithms, calibration algorithms, and coordinate transformation processing. These operations/processes may be executed directly on the tracking system computer 211 or executed on a separate computer (e.g., first device computer 208) in communication with the tracking system 206.

[0070] Bi-directional optical communication may occur between the 2-DoF device 100 and the tracking system 206 by way of a modulated light source (e.g., light emitting diode (LED)) and a photosensor (e.g., photodiode, camera). The 2-DoF device 100 may include an LED and a photosensor (i.e., a receiver) disposed on the working portion 104 or hand-held portion 102, where the LED and photosensor are in communication with a processor such as modem or an on-board device computer. Data generated internally by the 2-DoF device 100 may be sent to the tracking system 206 by modulating the LED, where the light signals (e.g., infrared, visible light) created by the modulation of the LED are detected by the tracking system optical detectors (e.g., cameras) or a dedicated photosensor and processed by the tracking system computer 211. The tracking system 206 may likewise send data to the 2-DoF device 100 with a modulated LED associated with the tracking system 206. Data generated by the tracking system 206 may be sent to the 2-DoF device 202 by modulating the LED on the tracking system 206, where the light signals are detected by the photosensor on the 2-DoF device 100 and processed by a processor in the 2-DoF device 100. Examples of data sent from the tracking system 206 to the 2-DoF device 100 includes operational data, surgical planning data, informational data, control data, positional or tracking data, pre-operative bone data, or instructional data. Examples of data sent from the 2- DoF device 100 to the tracking system 206 may include motor position data, battery life, operating status, logged data, operating parameters, warnings, or faults. In some embodiments, data generated by the first device computer 208 is sent to the tracking system 206, where that generated data is transferred to the 2-DoF device 100 via the LED on the tracking system 206.

[0071] It should be appreciated that in some embodiments of the present invention, other tracking systems are incorporated with the surgical system 200. By way of example but not limitation, the surgical system 200 may comprise an electromagnetic field tracking system, ultrasound tracking systems, accelerometers and gyroscopes, and/or a mechanical tracking system. The replacement of a non-mechanical tracking system with other tracking systems will be apparent to one skilled in the art in view of the present disclosure. In one form of the present invention, the use of a mechanical tracking system may be advantageous depending on the type of surgical system used such as the computer-assisted surgical system described in U.S. Pat. No. 6,322,567 assigned to the assignee of the present application and incorporated herein by reference in its entirety.

[0072] FIGS. 7A and 7B are schematic views showing the 2-DoF device 100 in greater detail. More particularly, FIG. 14A shows the 2-DOF device 100 in a first working POSE, and FIG. 14B illustrates the 2-DOF device 100 in a second working POSE. The 2-DoF device 100 comprises a hand-held portion 102 (or handle) and a working portion 104. The hand-held portion 102 comprises an outer casing 303 of ergonomic design which can be held and wielded by a user (e.g., a surgeon). In particular embodiments, the 2-DoF device 100 is intended to be fully supported by the hands of the user in that there are no additional supporting links connected to the 2-DoF device 100 and the user supports the full weight of the 2-DoF device 100. The working portion 104 comprises an end-effector 306 having an end-effector axis 307. The end-effector 306 may be removably coupled to the working portion 104 (via a coupler (e.g., chuck)) and driven by a motor 305. The hand-held portion 102 and working portion 104 are connected to one another, for example, by a first linear actuator 307a and a second linear actuator 307b in order to control the pitch and translation of the working portion 104 relative to the hand-held portion 102, as will hereinafter be discussed in further detail. In a particular embodiment, the working portion 104 is removably coupled to the hand-held portion 102 to permit different types of working portions to be assembled to the handheld portion 102. For example, a first working portion 104 may illustratively be a laser system having components to operate a laser for treating tissue, a second working portion 104 may illustratively be a drill for rotating a bone pin, and a third working portion 104 may illustratively be an oscillating saw.

[0073] A tracking array 312, having three or more fiducial markers of the sort well known in the art, is preferably rigidly attached to the working portion 104 in order to permit the tracking system 206 (FIG. 13) to track the POSE of the working portion 104. The three or more fiducial markers may, alternatively, be integrated directly with the working portion 104. The fiducial markers may be active markers such as light emitting diodes (LEDs), or passive markers such as retroreflective spheres. The 2-DoF device 100 may further include one or more user input mechanisms such as triggers (e.g., trigger 314) or button(s). The user input mechanisms may permit the user to perform various functions illustratively including: activating or deactivating the motor 305; activating or deactivating the actuation of the working portion 104 relative to the handheld portion 102; notifying the computing system 204 to change from targeting one virtual plane to a subsequent virtual plane; and pausing the surgical procedure.

[0074] Within the outer casing of the hand-held portion 102 is the a linear actuator 307a and a second linear actuator 307b. Each linear actuator (307a, 307b) may include a motor (310a, 310b) to power a screw (316a, 316b) (e.g., a lead screw, a ball screw), a nut (318a, 318b), and a linear rail (308a, 308b). In some inventive embodiments, the motors (first motor 310a, second motor 310b) are electric servo-motors that bidirectionally rotate the screws (316a, 316b). Motors (310a, 310b) may also be referred to herein as linear actuator motors. The nuts (318a, 318b) (e.g., ball nuts, elongated nuts) are operatively coupled to the screws (316a, 316b) to translate along the screws (316a, 316b) as each screw is rotated by its respective motor (310a, 310b). A first end of each linear rail (308a, 308b) is coupled to a corresponding nut (316a, 316b) and the opposing end of each linear rail (308a, 308b) is coupled to the working portion 104 via hinges (320a, 320b) such that the hinges (320a, 320b) allow the working portion 104 to pivot relative to the linear rails (308a, 308b). The motors (310a, 310b) power the screws (316a, 316b) which in turn cause the nuts (318a, 318b) to translate along the axis of the screws (316a, 316b). Translation of nuts 318a, 318b along ball screws 316a, 316b, respectively, causes translation of front linear rail 308a and back linear rail 308b, respectively, whereby to permit (a) selective linear movement of working portion 104 relative to hand-held portion 102, and (b) selective pivoting of working portion 304 relative to hand-held portion 302 of 2-DoF device 100. Accordingly, the translation “d” and pitch “a” (FIG. 14B) of the working portion 104 may be adjusted depending on the position of each nut (318a, 318b) on their corresponding screw (316a, 316b). A linear guide 322 (FIG. 14A) may further constrain and guide the motion of the linear rails (308a, 308b) in the translational direction “d”. In a particular embodiment, the nuts (316a, 316b) are elongated and couple directly to the working portion 104 via the hinges (320a, 320b), in which case the linear rails (308a, 308b) are no longer a component of the linear actuators (307a, 307b). It should be appreciated that other linear actuation mechanisms/components may be used to adjust the POSE of the working portion 104 relative to the hand-held portion 102 such as linear motors, pneumatic motors, worm drives and gears, rack and pinion gears, and other arrangements of motors and transmissions.

[0075] The 2-DoF device 100 may receive power via an input/output port (e.g., from an external power source) and/or from on-board batteries (not shown).

[0076] The motors (305, 310a, 310b) of the 2-DoF device 100 may be controlled using a variety of methods. By way of example but not limitation, according to one method of the present invention, control signals may be provided via an electrical connection to an input/output port. By way of further example but not limitation, according to another method of the present invention, control signals are communicated to the 2- DoF device 100 via a wireless connection, thereby eliminating the need for electrical wiring. The wireless connection may be made via optical communication. In certain inventive embodiments, the 2-DoF device 100 includes a receiver for receiving control signals from the computing system 204 (FIG. 13). The receiver may be, for example, an input port for a wired connection (e.g., Ethernet port, serial port), a transmitter, a modem, a wireless receiver (e.g., Wi-Fi receiver, Bluetooth® receiver, a radiofrequency receiver, an optical receiver (e.g., photosensor, photodiode, camera)), or a combination thereof. The receiver may send control signals from the computing system 204 directly to the motors (305, 310a, 310b) of the 2-DoF device 100, or the receiver may be in communication with a computer (e.g., an on-board device computer 209 as further described below) that processes signals received by the receiver and then generates the control signals for the motors (305, 310a, 310b) based on the received signals.

[0077] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0078] Various inventive concepts may be embodied as one or more methods, of which examples have been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. [0079] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[0080] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0081] The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0082] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0083] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0084] As used herein in the specification and in the claims, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

[0085] Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention. Any references to the “invention” are intended to refer to exemplary embodiments of the invention and should not be construed to refer to all embodiments of the invention unless the context otherwise requires. The described embodiments are to be considered in all respects only as illustrative and not restrictive.

Claims

CLAIMS What is claimed is:

1. A system for computer-assisted surgery comprising: a first device computer comprising at least one processor and at least one memory storing computer program instructions which, when executed by the at least one processor, performs computer processes for assessing native and/or planned joint gaps for a knee joint procedure to balance the knee in mid-flexion, wherein the computer processes include at least: determining one or more changes to a planned implant component position and/or orientation relative to a bone that achieves an intended spatial relationship to the gaps between the bones throughout the knee’s range-of-motion.

2. The system of claim 1, wherein the intended spatial relationship is a more rectangular shape compared to the shape of the distances prior to the changes.

3. The system of claim 1, wherein determining one or more changes comprises: changing different degrees of freedom either as individual degrees of freedom or in combination; and evaluating the resulting gaps.

4. The system of claim 1, wherein the computer processes include an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the gaps.

5. The system of claim 4, wherein determining one or more changes comprises permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function.

6. The system of claim 1, wherein the computer processes include an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component.

7. The system of claim 1, wherein each planned joint gap is measured as a distance from at least one point on a planned location for forming a cut surface on a tibial bone model to at least one point on a surface of a femoral implant model.

8. The system of claim 1, wherein the first device computer displays a graph that shows the distance for one or more of the gaps, together or separately, throughout the knee’s range-of-motion.

9. The system of claim 8, wherein the graph shows the gap distances between a planned location for forming a proximal cut surface on a tibia bone model to a planned location of an outer surface of a femoral implant model at a plurality of angles throughout the knee’s range-of-motion.

10. The system of claim 1, wherein assessing the gaps comprises affixing tracking arrays to the bones and tracking locations of the bones via the tracking arrays.

11. The system of claim 1, wherein the first device computer determines one or more alternative implant component positions and/or orientations based on the assessment of the native and/or planned joint gaps.

12. The system of claim 11, wherein the first device computer displays the alternate implant component positions and/or orientations relative to the bone models on a display device.

13. The system of claim 12, wherein the first device computer displays other informative data including measurements.

14. A method for computer-assisted surgery comprising: assessing, by a first device computer, native and/or planned joint gaps for a knee joint procedure and balancing the knee in mid-flexion including at least determining one or more changes to a planned implant component position and/or orientation relative to a bone that achieves an intended shape to the gaps between the bones throughout the knee’s range-of-motion.

15. The method of claim 14, wherein the intended spatial relationship is a more rectangular shape compared to the shape of the distances prior to the changes.

16. The method of claim 14, wherein determining one or more changes comprises: changing different degrees of freedom either as individual degrees of freedom or in combination; and evaluating the resulting gaps.

17. The method of claim 14, wherein the algorithm includes an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the gaps.

18. The method of claim 17, wherein determining one or more changes comprises permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function.

19. The method of claim 14, wherein the computer processes include an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component.

20. The method of claim 14, wherein each planned joint gap is measured as a distance from at least one point on a planned location for forming a cut surface on a tibial bone model to at least one point on a surface of a femoral implant model.

21. The method of claim 14, further comprising displaying a graph that shows the distance for one or more of the gaps, together or separately, throughout the knee’s range-of-motion.

22. The method of claim 21, wherein the graph shows the gap distances between a planned location for forming a proximal cut surface on a tibia bone model to a planned location of an outer surface of a femoral implant model at a plurality of angles throughout the knee’s range-of-motion.

23. The method of claim 14, wherein assessing the gaps comprises affixing tracking arrays to the bones and tracking locations of the bones via the tracking arrays.

24. The method of claim 14, further comprising determining one or more alternative implant component positions and/or orientations based on the assessment of the native and/or planned joint gaps.

25. The method of claim 24, further comprising displaying the alternate implant component positions and/or orientations relative to the bone models on a display device.

26. The method of claim 25, further comprising displaying other informative data including measurements.

27. A computer program product comprising a tangible, non-transitory computer readable medium having embodied therein software which, when run on a first device computer, performs the method of any one of claims 14-26.

28. A system for computer assisted surgery, comprising: a computer comprising at least one processor and at least one memory storing computer program instructions which, when executed by the at least one processor, perform processes comprising: determining locations of a first bone model and a second bone model that correspond to determined locations of a first bone and a second bone, respectively, as the first bone and the second bone are moved to a plurality of angles within a range- of-motion (ROM) of the first bone relative to the second bone; determining a distance between a point associated with the first bone model and a point associated with the second bone model for each angle from the plurality of angles using the determined locations of the first bone model and the second bone model; making adjustments to a planned location for a first implant model relative to the first bone model or a planned location for a second implant model relative to the second bone model; updating one or more distances between the point associated with the first bone model and the point associated with the second bone model in response to one or more adjustments; and identifying at least one planned location for the first implant model or planned location for the second implant model where the distances for two or more angles from the plurality angles achieves an intended spatial relationship.

29. The system of claim 28, further comprising a display for displaying the distances for at least two angles from the plurality of angles.

30. The system of claim 28, wherein the point associated with the first bone model is a point on a surface of a first implant model positioned on the first bone model.

31. The system of claim 28, wherein the point associated with the second bone model is a point on a planned location for forming a cut surface on the second bone model.

32. The system of claim 31, wherein the intended spatial relationship is a more rectangular shape than the shape of the distances before the adjustments.

33. The system of claim 28, wherein making adjustments, updating, and identifying is performed by an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the distances.

34. The system of claim 33, wherein determining one or more changes comprises permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function.

35. The system of claim 28, wherein making adjustments, updating, and identifying is performed by an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component.

36. The system of claim 28, further comprising: a tracking system for determining the locations of the first bone and the second bone as the first bone and the second bone are moved to the plurality of angles within the range-of-motion (ROM) of the first bone relative to the second bone.

37. The system of claim 36, wherein the tracking system determines the locations of the first bone and the second bone by determining the locations of a first tracking array affixed to the first bone and a second tracking array affixed to the second bone.

38. A method for computer assisted surgery, comprising: determining locations of a first bone model and a second bone model that correspond to determined locations of a first bone and a second bone, respectively, as the first bone and the second bone are moved to a plurality of angles within a range- of-motion (ROM) of the first bone relative to the second bone; determining a distance between a point associated with the first bone model and a point associated with the second bone model for each angle from the plurality of angles using the determined locations of the first bone model and the second bone model; making adjustments to a planned location for a first implant model relative to the first bone model or a planned location for a second implant model relative to the second bone model; updating one or more distances between the point associated with the first bone model and the point associated with the second bone model in response to one or more adjustments; and identifying at least one planned location for the first implant model or planned location for the second implant model where the distances for two or more angles from the plurality angles achieves an intended spatial relationship.

39. The method of claim 38, further comprising displaying the distances for at least two angles from the plurality of angles on a display device.

40. The method of claim 38, wherein the point associated with the first bone model is a point on a surface of a first implant model positioned on the first bone model.

41. The method of claim 38, wherein the point associated with the second bone model is a point on a planned location for forming a cut surface on the second bone model.

42. The method of claim 41, wherein the intended spatial relationship is a more rectangular shape than the shape of the distances before the adjustments.

43. The method of claim 38, wherein making adjustments, updating, and identifying is performed by an optimizer algorithm that defines a cost function of difference from the intended spatial relationship for the distances.

44. The method of claim 43, wherein determining one or more changes comprises permuting positions or orientations of a femoral implant model and/or a tibial implant model in one or more degrees-of-freedom (DoF) relative to their respective bone models to get a minimum cost from the cost function.

45. The method of claim 38, wherein making adjustments, updating, and identifying is performed by an optimizer algorithm that includes an artificial intelligence (Al) or machine learning (ML) algorithm component.

46. The method of claim 38, further comprising: using a tracking system to determine the locations of the first bone and the second bone as the first bone and the second bone are moved to the plurality of angles within the range-of-motion (ROM) of the first bone relative to the second bone.

47. The method of claim 46, wherein the tracking system determines the locations of the first bone and the second bone by determining the locations of a first tracking array affixed to the first bone and a second tracking array affixed to the second bone.

48. A computer program product comprising a tangible, non-transitory computer readable medium having embodied therein software which, when run on a first device computer, performs the method of any one of claims 38-47.